Milling machine

ABSTRACT

The improved milling machine makes use of individually controlled x-axis, y-axis, and z-axis carriages. These carriages provide positive and precise control of the position of the cutting tools and the blank to be cut. A tool changer allows the tools to be changed to accommodate other materials. A camera is used to detect wear on the tools.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an improved milling machine that isused to mill a crown or dental implant from a blank. The milling machineis adapted to receive instructions from a separate scanner that providesa memory in the milling machine with data on the outer and innercontours for the milled crown.

BACKGROUND TO THE INVENTION

One of the most common procedures for a dentist is the repair of abroken tooth. When a tooth is broken, a portion of the enamel comes off,exposing the dentin underneath. The dentin must be covered to preventthe dentin from becoming infected. The dentist will grind a portion ofthe remaining enamel away to prepare the tooth for a crown. Once thegrinding procedure is complete, a reduced stump remains and a mold ofthe stump is made with a quick setting mold material. Further a mold ofthe adjacent teeth and the opposing teeth are also made. Then atemporary crown in placed on the stump. The temporary crown has beenpartially customized to fit over the stump and to mesh with the opposingteeth. However, due to traditional time constraints, the temporary crownrarely feels as natural as the original tooth. Further, the temporarycrown must be affixed to the stump with a temporary fixative.

With the mold as a guide, an outside laboratory will prepare a permanentcrown. The permanent crown may be made of porcelain, gold, ceramic, orother metal or substance. This process usually takes at least threeweeks to complete. During this time, the patient must function with thetemporary crown. Unfortunately, there is a risk that the temporary crownmay loosen and be swallowed or otherwise lost by the patient. Even if itonly loosens, bacteria can gain access to the dentin for a time andcause more serious dental health issues. Also, once the permanent crownis available for placement, the temporary crown must be removed. Thisrequires the dentist to twist the temporary crown off the stump,exerting a significant torque to the roots. Even then, if the permanentcrown is misshaped, then it may need to be removed again and remade.

A need exists for a method of improving the speed of producing apermanent crown for a patient. Indeed, if the crown could be producedwhile the patient waited, it would be a great savings for the patientand the dentist both. Moreover, it would also be beneficial to eliminatethe need to make a temporary crown at all.

Sirona Dental Services GmbH, of Bensheim Germany produces a millingmachine specifically for producing porcelain crowns. It is disclosed inU.S. Pat. No. 6,394,880 discloses one aspect of this milling machine. Itallows for the use of two milling bits to simultaneously work a blank toform it into a permanent crown. The mill bits are located on oppositesides of the blank and can move in an x-, y-, and z-plane. However, thebits can not be changed on demand to accommodate a different blankmaterial. Also, there is no method disclosed for determining the bitwear to warn the dentist that the crown's dimensions may be skewed dueto bit wear.

The Sirona patent illustrates a portion of a larger milling machineknown as the CEREC. The CEREC has several other drawbacks. First, it hasonly a wireless connection with an intraoral digitizer used to make themeasurements of the stump and adjacent teeth. Once the measurements aremade, the intraoral digitizer cannot be used until the crown isfinished. Therefore, a need exists for a milling machine that includes amemory that can store the required data thereby freeing the intraoraldigitizer to be used again. Further, the CEREC device is flawed in itsfailure to minimize vibration that affects the quality of the milling.Even minor vibration can create many microns of error on the surface ofthe crown.

SUMMARY OF THE INVENTION

The present invention overcomes many of the defects of the prior art andallows the dentist to mill a superior permanent crown or other dentalinlay while the patient waits. This reduces the amount of time for thepatient in the dentist chair, thereby allowing the dentist to schedulemore patients. Further, it is a significant time savings for thepatient. The milling machine can be located at the dentist office.However, it could also be located at a traditional dental lab. In thisevent, the lab would receive the data outlining the contours for thecrown or the inlay. It would still be able to supply a superior crown orinlay in less time than traditionally experienced.

The present milling machine is characterized by a robust and sturdyframe that minimizes any vibration. This helps ensure the highestquality end product. Further, the spindles that rotate the milling bitsare located on a common rail, giving the device the ability to move thetools in the x-axis. The blank is releasably attached to a mandrel. Themandrel is secured to a subassembly that allows motion in the y-axis andthe z-axis. The milling machine includes a CPU and memory for storingthe data on the contour of the crown or inlay. Further, the millingmachine has a water reservoir for settling any particulate that becomesentrained in the water used to cool and rinse the blank during milling.

Tools used to mill the blank can be changed using a novel automatic toolchanger. The ability to engage different tools also allows for the useof different blank materials, from hardened metals to ceramics toporcelain to gold. Further, a camera or other sensing device can be usedto monitor wear experienced by the tools. The blank is held by a mandrelthat engages a frame within a work area that is easily accessible to atechnician or the dentist. While this disclosure focuses on theproduction of crowns, it should be understood that this term is beingused broadly. Indeed, while a crown is one of the preferred items formilling, this improved milling device could be used to produce inlays,onlays, coping, framework, bridges, implants, implant abutments,veneers, and overlays.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbest be understood by reference to the following detailed description ofan illustrative embodiment when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a perspective view of a milling machine that embodies thepresent invention;

FIG. 2 is perspective showing the carriage that controls the x-axismovement of the spindles;

FIG. 3 is a cut-away view of the spindle showing the collet that engagesthe cutting tool and the cooling fluid delivery path;

FIG. 4 is a perspective view of the subassembly that controls the y-axisand z-axis of the device;

FIG. 5 is an enlarged view showing the automatic tool changing machineand the digital camera used to detect tool wear and axial calibration;

FIG. 6 is an enlarged perspective showing the engagement between thetool in a spindle and the automatic tool changer;

FIG. 7 is a perspective view of a tool that can be used in the presentembodiment;

FIG. 8 is an exploded view of the mandrel and blank.

DETAILED DESCRIPTION OF THE DRAWINGS

This inventive milling machine is sized to fit on the countertop of adentist office or in a lab. Its generally compact size however does notmean that the quality of end product is diminished. Instead, the millingmachine is built so robustly that it will produce the highest qualitycrowns and inlays. An intra-oral digitizer is used to measure thedimensions of the prepared tooth, as well as the adjacent and opposedteeth. Software within the digitizer constructs an outer contour thatmeshes with the adjacent and opposing teeth. The design is approved bythe dentist and then conveyed to the milling machine.

FIGS. 1 and 2 provide perspective views of the milling machine 100. Itincludes a cover 102 that protects the operator from the moving partswithin. A blank 10 is held within a work area that is accessible throughdoor 104. The x-axis carriage 110 is used to move the tools back andforth into engagement with the blank 10. The carriage 110 includes afirst and second frame that both slide on rails on subframe 112. Thesubassembly 140 is used to control the y-axis and z-axis movement of themandrel and blank. A reservoir is also located at the bottom of themachine 100. The CPU, memory and other electronics are located incompartment 107. These can be controlled, or activity displayed ondisplay 106.

FIG. 2 is an isolated view of the x-axis carriage 110. It includes afirst frame 114 and a second frame 116. In one embodiment, these framesare formed from a single block of metal, having no seems to decreasetheir stiffness. A first and second spindle 118, 120 are coupled tothese frames 114, 116. The frames 114, 116 move on a single pair ofrails 122 to ensure absolute alignment. Each frame is coupled to a firstand second spindle, wherein each spindle has a central axis. The centralaxis of each spindle are aligned. Tools 128 and 130 are accepted intothe spindles along this axis. The spindles rotate the tools so that acutting surface on the tool can carve away material from the blank asdesired. Of course, this process generates heat and carvings. A fluidstream emits from the spindle ports 126 as well to wash and cool theblank during milling. This effluent exits to a reservoir whereparticulate matter can settle. Motors 124 are used to supply the powerto move the frames along the rails and to rotate the tools within thespindles.

FIG. 3 provides a more detailed view of the spindle 120 and the tool130. Water, or other cooling fluid, is fed into the spindle throughsupply 124. Water passes through passages 132 into a collar 136. Thiscollar supplies the water into several tubes 138 that carry the water tothe front of the spindle. The water is sprayed from the tips of thetubes 138 and directed toward the tip of the tool 130. At least oneo-ring is used to seal and separate the spindle's motor from the water.

The complex outer contour of the damaged tooth is reproduced by thepresent milling machine. This requires an accurate understanding ofexactly the location of the tip of the tools and the x, y, z coordinatesof the blank. Thus the shape and length of the mandrel 160 holding theblank must be precise. Very precise motors are used to move thecarriages shown in FIG. 3. This same level of precision is reproducedfor the y and z axes. However, rather than move the spindles, themandrel is moved in the y and z axes by the subassembly 140 shown inFIG. 4. In FIG. 4, the y-axis is controlled by moving a carriage alongrails. A separate z-axis carriage 142 includes the frame for engagingthe mandrel 160 and automatic tool changer 130. This view alsoillustrates the location of the mandrel 160 and blank 10 to be milled.It is located on the z-axis carriage. A cam 162 is used to secure themandrel in place. The mandrel and blank will be shown in greater detailbelow. The automatic tool changer 150 is also attached to the z-axiscarriage. The tool changer can carry several additional tools 128, 130for placement into the spindles. The tool changer 150 also includes atleast one open port 154 for accepting the tool in the spindle. Anelectronics package 152 can be located on the end of the tool changer150.

FIG. 5 provides an even more detailed view of the tool changer 150,blank 10, and tools. In this view, the y-axis carriage has moved theblank 10 above the tool 128. In this position, a camera 170 can be usedto inspect the condition of the tip of tool 128. Note that the tool 128is co-axially located within the spindle 118. Further, note that thenozzles 126 are angled to direct a cooling spray of fluid onto the tipof the tool 128.

One of the important advances of the present invention is the ability tosubstitute tools as required. For example, a tool for grinding a contouronto a ceramic is different than a tool for grinding a contour onto ablank of gold. The prior art has never addressed the need for a lab tobe able to quickly deal with blanks of differing materials. The presentinvention can allow a technician to simply enter the desired material.The milling machine will engage the appropriate tool for the material.The camera 170 will inspect the tool for wear and if necessary, select abackup tool for the process. Alternatively, if the tool is too worn andno back-up is available, the technician will be alerted. The ability toengage and disengage the tools is shown in FIG. 6. The tool changer 150is positioned with the y-axis carriage to a position in between thespindles. The selected tool is positioned in co-axial relationship withthe spindle using the z-axis carriage. A collet on the spindle is openedto engage the distal end of the tool, for example tool 130. The tool isreleasably secured in the tool changer 150 with a spring loaded ball 172or other means for securing the tool. Ball 172 presses against a centralportion of the tool between a first and second flange. When the tool isengaged in the spindle, its collet closes. The tool changer 150 is thenlowered with the y-axis carriage. This forces the ball 172 against pin174 and compressed spring 176. The force on spring 176 can be adjustedusing the set screw 178.

FIG. 7 provides a more detailed illustration of the tool 130. Itincludes a distal end 130 a that is engaged within the spindle. At least25% of the length of the tool is engaged within the spindle to ensurestability and to minimize and bending of the tool. The proximal end 131of the tool can vary based on the material to be milled. For example,the grinding tip shown is for a ceramic. However, another tip might beused for grinding away a metal blank. Flanges 130 b and 130 c define acentral portion that is used to engage the tool to the tool changer 150.However, the flanges serve the additional purpose of assisting with theregistration of the tool and the blank. In other words, even though theexact length of the tool is known, the x, y, z coordinates of its tipmust still be known exactly. When the tool is engaged into the spindle,the flange acts as a travel limit and thus defines the distance betweenthe tip and the spindle. Thus, when the spindle moves along the x-axis,the position of the tip of the tool will be known.

In addition to knowing the exact x, y, and z coordinates of the tooltips, it is also essential to know the exact position for the blank.This requires that the mandrel and blank be consistently placed into themachine. The mandrel and blank engage a mandrel socket 164 that in turnengages the z-axis carriage. FIG. 8 shows the mandrel socket in moredetail. The mandrel 160 has a distal end that enters a similarly shapedsocket 164. As shown the mandrel has a generally circular cross-sectionthat engages the generally cylindrical socket. A groove 166 near thedistal end of the socket provides an engagement surface for a cam 162.The cam 162 is rotated to a first position to allow insertion of themandrel 160. The cam 162 is then rotated to a second position thatengages the groove and secures the mandrel within the socket. A pin 168is used to prevent the accidental rotation of the cam. While acylindrical mandrel is shown, its cross-section could be any suitableshape. Note that the socket has an opening on both ends. This allows fordebris to be pushed through the socket rather than allow it to build upwithin the socket.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of theinvention. Accordingly, the invention is not to be restricted except inlight of the attached claims and their equivalents

1-12. (canceled)
 13. A method of milling a blank using an improvedmilling machine comprising the steps of: (a) inserting a blank into themilling machine; (b) selecting a contour for the blank; (c) milling theblank to match the contour using three tools that are manipulated on anx-carriage, a y-carriage, and a z-carriage.
 14. The method of claim 13wherein the step of inserting the blank comprises fixing the blank bymeans of a mandrel into a mandrel socket.
 15. The method of claim 13wherein the step of selecting a contour for the blank comprises thesteps of receiving data from an intra-oral digitizer.
 16. The method ofclaim 13 wherein the step of milling the blank comprises selecting afirst and second tool for milling.
 17. The method of claim 16 whereinthe step of milling the blank further comprises inserting the first andsecond tool into a first and second spindle coupled to the x-axiscarriage.
 18. The method of claim 17 further comprises advancingspindles along the the x-axis into contact with the blank.
 19. Themethod of claim 17 further comprises positioning the blank using they-axis and z-axis carriages.